1. Field of the Invention
The present invention relates generally to photographic printing systems and, more particularly, to photographic printing systems that can read data recorded in a magnetic recording material of a photographic filmstrip.
2. Description of the Related Art
Data recording photographic cameras have magnetic write heads that write data on recordable photographic filmstrips as frames of latent images are exposed. After the filmstrip is developed, the data can be retrieved by a magnetic read head of a photographic printer. Such data can comprise, for example, data relating to the exposure parameters used by the camera when exposing the frame, a camera identification number, and the date of producing the exposure. As a developed filmstrip is passed through a suitably equipped photographic printer to produce finished prints, the magnetic read head of the printer reads the data from the filmstrip. The recorded exposure data can be used by the printer in setting printer parameters, such as color balance, and the identification and date data can be printed on the finished prints as a matter of interest to the photographer.
The recordable photographic filmstrip used in a data recording camera includes a magnetic recording material that is deposited on the filmstrip or is integrally formed with the film emulsion or substrate. Generally, the magnetic recording material is deposited in a thin transparent layer over the entire surface of the photographic filmstrip and is referred to as the magnetics-on-film (MOF) layer. As frames are exposed in the data recording camera, the data is recorded into the MOF layer of the filmstrip in longitudinal data tracks that typically extend along one edge of the filmstrip outside of the frames.
To read the recorded data from the developed filmstrip, a photographic printer must include a head assembly having a magnetic read head. The magnetic read head must be positioned accurately over the data tracks of the MOF layer and must be maintained in proper position over the data tracks as the filmstrip is moved through the printer. As the filmstrip is moved, relative movement occurs between the filmstrip and the magnetic read head. Ideally, the read head remains located above the longitudinal data tracks and therefore can accurately read the data. If the relative movement produces lateral displacement between the magnetic read head and the data tracks, inaccurate reading of the recorded data can occur.
One technique for reading data from the MOF layer of a recordable photographic filmstrip is to provide the head assembly of the photographic printer with a guide plate that is oriented perpendicular to the edge of the filmstrip and is pressed against the edge. The filmstrip is kept under tension and therefore remains substantially taut against the pressure. The data tracks are recorded in the filmstrip MOF layer at a predetermined distance from the edge because, in a data recording camera, the magnetic write head is located a predetermined distance from the edge of the path followed by the filmstrip in the camera. Therefore, in the photographic printer, the magnetic read head can be located a predetermined distance from the guide plate such that the read head is properly positioned over the data tracks when the guide plate is in contact with the edge of the filmstrip.
For example, if the edge of a recordable photographic filmstrip closest to the top of the frames is defined to be the top edge, then the filmstrip may have a sequence of data tracks written along the lower edge. As the filmstrip is moved through the printer, the guideplate is urged upwardly against the bottom edge of the filmstrip. Further upward movement is prevented by the guide plate rubbing up against the taut edge of the filmstrip, and the magnetic read head thereby is properly positioned over the data tracks. Unfortunately, such guide plates can damage the filmstrip and cause excessive wear because of the friction and pressure generated by the guide plate as it presses against the filmstrip.
Some optical techniques are known outside the photographic field for properly positioning magnetic read heads above data tracks recorded in magnetic storage media, such as magnetic tapes or disks. The optical techniques improve read head tracking in the magnetic storage media and do not require physical contact with the magnetic media for proper tracking. Therefore, they do not cause damage or excessive wear. Such techniques, however, make use of specially prepared magnetic media that incorporate optical patterns in the magnetic media and are not intended for use with photographic filmstrips. Such techniques reduce the surface area of the magnetic media that can be used for other purposes. See, for example, U.S. Pat. No. 4,987,505 to Iwabuchi, et al. and U.S. Pat. No. 4,816,939 to Ford, et al. Such techniques, if adapted for use with photographic filmstrips, would reduce the area of the filmstrip available for the photographic image frames.
Other optical techniques for use with magnetic media include a pair of light-emitting elements placed beneath the top and bottom edges of the magnetic media. Corresponding light-receiving elements of a magnetic head assembly detect variations in the relative amounts of light received from the emitters and generate positioning control signals. Such techniques require that the light receiving and emitting elements straddle the magnetic media. Therefore, the magnetic media must be of predetermined, constant width. See, for example, U.S. Pat. No. 4,176,381 to de Niet, et al. Variations in the width of the magnetic media cannot easily be accommodated. Such techniques, if adapted for photographic printers, would limit the processing of multiple film formats.
From the discussion above, it should be apparent that there is a need for a system that accurately maintains a magnetic head of a photographic printer in proper position over magnetic data tracks recorded in a magnetic recording material of a photographic filmstrip without damaging the filmstrip or causing excessive wear and without requiring specially prepared, optically encoded filmstrips. The present invention satisfies this need.